on the 2013 sunseeker 3050s there is a black swich on the lower bottom of the left side drivers seat. only shows a battery with positive and negitive symbols. nothing in the book on what it is. to the dealership, they never had one of these coaches before, so they said all is new to them. anyone have an idear of what this is

Yes, what lkin said. If your engine battery is dead, hold the switch in and it connects the engine battery to the coach batteries so you can start the engine. On my 2250, if the coach batteries are dead and I start the engine, after about 30 seconds a relay automatically connects the coach and engine batteries so I can start the generator.
Lou